"The cups were confiscated before they came in contact with any children," Kiddie Academy administrators wrote in a statement.

Hoefling said investigators are trying to determine if Gratz ever drugged toddlers with the sleeping aid before.

Gratz was a full-time teacher at Kiddie Academy for five years. Her primary responsibility was a class of toddlers who are 1 and 2 years old.

A witness saw Gratz place an unknown substance into some of her students' drinking cups on Friday, Hoefling said. Gratz was confronted by facility administrators and admitted that the substance was Sominex, police said. Sominex is an over-the-counter sleeping aid that is available at pharmacies.

On Monday, a search warrant was served on Gratz' Hollister home and investigators seized evidence. Gratz was placed under arrest on felony child endangerment charges and she was booked into the Santa Clara County main jail.

Investigators said they are still attempting to establish a motive.

Anyone with information regarding this incident or believes their child was under the care of Gratz while at the Kiddie Academy is urged to call Morgan Hill Police Department Detective Joe Burdick at 408-779-2101.

"The safety and welfare of children is our top priority. We have an exceptionally qualified staff of teachers who have chosen early childhood education because of their love of working with children," Kiddie Academy spokeswoman Rose Chin said. "Ms. Gratz was terminated immediately for her actions and we are fully cooperating with authorities on this case."

PHOTOS: Morgan Hill teacher drugged students with Sominex, police say

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A teacher at a Morgan Hill daycare center was fired and arrested after she was accused of drugging toddlers with Sominex. Deborah Gratz, 59, of Hollister, was fired after it was alleged that she put a sleep drug into several children’s drinking cups, police said.